1. Field of Invention
The present invention relates to bicycles and, more particularly, pertains to bicycle rear suspensions.
2. Description of Prior Art
Generally, rear suspensions for mountain bicycles comprise shock absorber systems including various types of springs and shock absorbing devices, and a pivot system defining the path of the rear wheel upon impact thereof with an uneven ground surface.
Simple bicycle rear suspension designs essentially comprise a main pivot located on a main frame of the bicycle for pivotally connecting thereto a swingarm or a rear frame portion. According to this type of rear suspension, the rear wheel pivotally moves in a circular path of constant radius about a single axis of rotation which is fixed relative to the main frame of the bicycle. This first category of bicycle rear suspensions may be embodied in different forms and configurations, such as the xe2x80x9cMacPherson Strutxe2x80x9d (see xe2x80x9cFirst Dirt for Proflex 855xe2x80x9d, Mountain Bike Action, February 1995, pp. 51-55; and xe2x80x9cLes suspensions arrixc3xa8re: Des forces à domestiquerxe2x80x9d, Yannick Boivin, Vxc3xa9lo Mag, Spring 1996, pp. 38-40) and its variants; the xe2x80x9ccantilever beamxe2x80x9d (see xe2x80x9cFoes Fab Weaselxe2x80x9d, Mountain Bike Action, September 1995, pp. 49-60); and the xe2x80x9cfloating drivetrainxe2x80x9d (see xe2x80x9cFloating Drivetrain Kleinxe2x80x9d, Mountain Bike Action, February 1995, pp. 67-70).
Other types of bicycle rear suspensions are provided with more sophisticated linkage systems comprising upper and lower links adapted to pivotally connect the swingarm to the front frame portion of the bicycle such as to allow the rear wheel to travel in a different arc than with a single link system (see xe2x80x9cxe2x80x9cFloating GT""s Fully Active LTSxe2x80x9d, Mountain Bike Action, February 1995, pp. 56-63; xe2x80x9cDual Suspension bike of the decade?xe2x80x9d, Vic Armijo, Guide to Suspension and high performance, volume 2, 1996, pp. 11-12; and U.S. Pat. Nos. 5,259,637 and 5,306,036 issued to Busby on Nov. 9, 1993 and on Apr. 26, 1994, respectively). More particularly, these two Busby U.S. Patents disclose a bicycle rear suspension linkage system comprising two upper pivots and two lower pivots which are rigidly interconnected to constrain the motion of a swingarm with respect to a main bicycle frame. The unique rear wheel axle path upon impact of the rear wheel on an obstacle is thus determined by the relative positions of the upper and lower pivots. Busby""s bicycle rear suspension linkage system further comprises a shock absorber which is adapted to limit the amplitude of the motion of the rear wheel axle without having any influence on the trajectory thereof.
U.S. Pat. No. 5,405,159 issued to Klein et al. on Apr. 11, 1995 discloses a suspension system comprising a rotating damper link pivotally connected at a first end thereof to an upper portion of a main frame and at a second end thereof to an upper portion of a swingarm, and a composite spring disposed between lower portions of the main frame and swingarm. The composite spring is designed to act as a rigid link in a horizontal plane and thus only one variable is needed to specify the position of the rear wheel axle in the plane of the bicycle frame.
Therefore, there is a need for a bicycle suspension system which allows the rear wheel axle to follow various paths in response to, and depending from, various obstacles encountered by the bicycle""s rear wheel.
It is therefore an aim of the present invention to provide a rear suspension having two degrees of freedom and which is particularly suitable for bicycles including mountain bikes.
It is also an aim of the present invention to provide a rear suspension which allows a rear wheel to define different trajectories according to the type of obstacles encountered by the rear wheel of the bicycle.
Therefore, in accordance with the present invention, there is provided a rear suspension system for a bicycle having a main frame and a swingarm supporting a rear wheel axle about which a rear wheel may rotate, comprising link means pivotally mounted at two spaced-apart locations to said main frame and to said swingarm, and biasing means for normally urging said swingarm and said main frame in a relative equilibrium position, while allowing said rear wheel axle to move along various paths relative to said main frame in response to different shock forces exerted on the rear wheel.
Also in accordance with the present invention, there is provided a rear suspension system for a bicycle having a main frame and a swingarm, comprising a substantially rigid link means having a first end portion thereof pivotally connected to the main frame and a second opposed end portion thereof pivotally connected to the swingarm, and shock absorber means adapted to cooperate with said link means for substantially constricting relative motions of the main frame and the swingarm to two independent directions.
Further in accordance with the present invention, there is provided a rear suspension system for a bicycle having a main frame and a swingarm, comprising a substantially rigid link means pivotally mounted at two spaced-apart locations to the main frame and to the swingarm, and resilient connecting means mounted between the main frame and the swingarm for normally urging the main frame and the swingarm in a relative equilibrium position, while enabling said rear suspension system to have two degrees of freedom.
Still further in accordance with the present invention, there is provided a bicycle frame, comprising a main frame, a swingarm supporting a rear wheel axle about which a rear wheel may be mounted, a rear suspension system comprising link means pivotally mounted at two spaced-apart locations to said main frame and to said swingarm, and biasing means for normally urging said swingarm and said main frame in a relative equilibrium position, while allowing said rear wheel axle to move along various paths relative to said main frame in response to different shock forces exerted on the rear wheel.
More specifically, the bicycle frame includes a pedal crankset assembly mounted to a lower portion of said swingarm, said link means being pivotally mounted at a first end portion thereof to a lower rear portion of said main frame for rotation about a first pivot axis, said link means being pivotally mounted at a second end portion thereof to a lower front portion of said swingarm for rotation about a second pivot axis, said second pivot axis being located above or below a principal axis of the bicycle when said main frame and said swingarm are in said relative equilibrium position, said principal axis extending through said first pivot axis and parallelly to a bicycle axis extending through the front and rear wheel axles of the bicycle.
Also, the second pivot axis may be located in front of the pedal crankset assembly.
Alternatively, the bicycle frame may include a pedal crankset assembly mounted to a lower portion of said main frame, said link means being pivotally mounted at a first end portion thereof to a lower rear portion of said main frame for rotation about a first pivot axis, said link means being pivotally mounted at a second end portion thereof to a lower front portion of said swingarm for rotation about a second pivot axis, said first pivot axis being located below the pedal crankset assembly.
Furthermore, the biasing means may have two degrees of freedom.
Moreover, the biasing means include spring means and damper means extending between said main frame and said swingarm, said spring means being adapted for deflection in two at least partially independent directions in a plane containing said main frame and said swingarm.
Specifically, the spring means comprise a leaf spring located above said link means. The spring may include an upwardly arcuate portion, said leaf spring being adapted to be rigidly attached at a first end portion thereof to an upwardly extending rear member of the main frame and at a second opposed end portion thereof to an upper member of the swingarm.
Alternatively, the leaf spring may have a substantially inverted U-shaped configuration, said leaf spring being adapted to be rigidly attached at a first end portion thereof to an upwardly extending member of the main frame and at a second opposed end portion thereof to an upwardly extending front member of the swingarm.
Typically, the damper means are pivotally connected at opposed end portions thereof to the main frame and to the swingarm.